The present invention relates to sealing glass compositions. More particularly, the invention relates to sealing glass compositions for bonding ceramics and still more particularly to compositions useful in bonding ceramics with satisfactory bond strength even when fired at temperatures of less than 400.degree. C.
Semi-conductor devices or chips, also known as "dies", are packaged in hermetically sealed ceramic containers to resist breakage and destruction. Such ceramic packages may be made of alumina, silicon carbide, silicon nitride, or other ceramics. A common packaging material is alumina (Al.sub.2 O.sub.3).
Ceramic packages of the type described are typically sealed by applying a sealing glass composition to the surfaces of the ceramic components and then heating them to elevated temperatures to effect bonding. One problem which has arisen in connection with such ceramic packages is that the sealing glass compositions heretofore known have typically required firing at temperatures of 400.degree. C. or higher to achieve bonding of the ceramic components with satisfactory bond strength. For example, sealing glasses based on lead borate systems, such as have been commonly used, required firing at 430.degree. C. to produce the desired bond strength. However, many of the new semi-conductor dies are much more sensitive to firing temperature and their usefulness will be adversely affected by exposure to temperature over 400.degree. C. Dies which are sensitive to firing temperature include larger dies and dies employing fine line geometry. In the latter case, lines of Si-SiO.sub.2 -Si which are spaced 1 to 2 microns apart are provided at the die surface. Firing at high temperatures to accomplish bonding tends to destroy the usefulness of these dies due to incipient melting of the line compositions which may result in undesirable contact between the lines.
It is therefore desirable to be able to provide a ceramic package which does not require firing at these elevated temperatures to achieve satisfactory bond strength.